This invention relates to a method for the production of reinforced composites from compositions which are photopolymerisable and thermosettable and from fibrous reinforcing materials, and to the composites obtained by this method.
Composite structures are commonly made by impregnating fibrous materials, such as paper, glass, and carbon fibres, with a solution of a solid thermosettable resin and a heat-activated curing agent for the resin, causing the resin to solidify by evaporation of the solvent, and, when desired, curing the resin composition by the action of heat. Composite structures may also be prepared from films of a thermosettable resin composition by the method described in British Pat. No. 1,299,177, which comprises laying a film of the resin composition on a fibrous reinforcement and applying heat and pressure so that the resin composition flows about the fibres but remains curable, and then heating further when desired so that the resin composition is cured by the heat-activated curing agent. The latter procedure is particularly convenient when unidirectional fibrous reinforcement is to be used, especially if the fibres are short and/or light, because there is less tendency for the fibres to become displaced and the reinforcing effect thereby become irregularly distributed. Both these methods suffer from certain drawbacks. If a solvent is used, it is not always possible to eliminate all traces of it before the final curing takes place, and in consequence the final composite may contain voids caused by evaporation of such residual solvent. Further, use of solvents may cause difficulties due to their toxicity or inflammability or to pollution. When a film adhesive is used, it is usually cast from a liquid thermosettable resin and this then advanced to the solid state, and such a process adds considerably to the cost of the composite. Both methods also require a considerable expenditure of heat energy, either to evaporate the solvents or to advance the resin.